This invention relates to optical arrangements for illumination of the surface of a optical biosensor and the detection of interactions, typically biochemical interactions, occurring on the surface of the biosensor.
The applicant's assignee SRU Biosystems, Inc. of Woburn, Mass. has developed and commercialized a label-free photonic crystal optical biosensor in which the surface of the biosensor includes a periodic surface grating. The biosensors are described in the patent literature, see for example U.S. patent application publications U.S. 2003/0027327; 2002/0127565, 2003/0059855 and 2003/0032039, the content of which is incorporated by reference herein.
SRU Biosystems has also developed a reading instrument for the biosensors. The reading instrument includes a light source (which can take the form of a white light source) and an optical arrangement for directing the light from the source to the surface of the biosensor at normal or near normal incidence. The optical arrangement also directs light reflected from the surface of the biosensor to a spectrometer or other instrument for detecting the peak wavelength (PWV) of the reflected light. Biochemical interactions occurring on the surface of the biosensor cause a change in the index of refraction of the biosensor surface, which results in a small shift in the PWV. The optical arrangements in the detection instrument are shown in the above patent documents. Briefly, the optical arrangement uses a 45-degree beam splitter cube to pass illumination upward to the biosensor and then to reflect light returning from the sensor to the spectrometer entrance slit. Each passage of the light through the beam splitter reduces the light intensity by half. Since the light passes through the beam splitter twice, there results an overall four-fold reduction in intensity of light impinging on the spectrometer.
This invention provides an optical arrangement for illumination and detection of a biosensor which eliminates the need for a beam splitter to direct the incident and reflected light. This increases the light efficiency four-fold as compared to the beam splitter arrangement described in the above-referenced patent documents.